Sound translating device with resonating and damping chamber



March 16, 1954 c, PYE 2,672,525

SOUND TRANSLATING DEVICE WITH RESONATING AND DAMPING CHAMBER Filed June16, 1950 2 Sheets-Sheet l INVENTOR. HAROLD C. PYE

ATTORNEY H. c. F'YE NG DEVICE WITH RESONATING March 16, 1954 SOUNDTRANSLATI AND DAMPING CHAMBER 2 Sheets-Sheet 2 Filed June 16, 1950 FIG.5

26o 460 c lo'oo zo'o o 40'00 INVIISQ'TOR U "A e req ency yc es per 5 conBY Z O u n w 0 o m m w 8 82:22 0 303 22:80 E 2:32,... .ucaom ATTORNEYPatented Mar. 16, 1954 SOUND TRANSLATING DEVICE WITH RESO- NATING ANDDAMPING CHAMBER.

Harold C. Pye, Oak Park, 111., assignor to Automatic ElectricLaboratories, Inc., Chicago, 111., a corporation of Delaware ApplicationJune 16, 1950, Serial No. 168,630

Claims.

The present invention relates in general to sound translating devicesand methods of making the same and moreparticularly to improvements intelephone receivers of the permanent magnet type and methods of makingthe same.

It is an object of the present invention to provide an improved soundtranslating device which is of extremely simple, economical, lightweight, and rugged construction, is compact in arrangement, and iseflicient in operation.

It is another object of the invention to provide an improved soundtranslating device which has a uniform frequency response over a greaterrange than heretofore.

In general, the objects as set forth above are in part attained inaccordance with the present invention by providing a sound translatingdevice which includes a plastic cup shaped housing; two pole pieces, theends of which are molded into the housing; a permanent Alnico bar magnetseparating the pole pieces and completely molded or rather imbedded inthe housing; a diaphragm; a front resonating chamber so constructed anddimensioned that its natural acoustic resonating frequency isapproximately 4000 cycles per sec- 0nd; and a damping means in thatfront chamber for decreasing the peak amplitude at that naturalfrequency. Briefly explained, the frequency response range is firstextended by effecting a natural resonant peak at 4000 cyclesand then byflattening the natural peak ordinarily produced by such resonance, theresponse curve is made practically uniform from 200 to 4000 cycles persecond.

A feature of the improved sound translating device is the arrangement ofthe permanent magnet within the plastic housing such that magnetizationmay be accomplished after the complete assembly of the receiver unit;thus eliminating foreign magnetic particles within the field structurethat may be attracted during the assembly of a magnetized bar magnet.

Other objects and features will be evident and a com lete understandingof the construction and operation may be had from a perusal of thedescription in conjunction with the accompanying drawings, in which:

Fig. 1 shows a side sectional view of the sound translating device takenalong the line AA of Fig. 2.

Fig. 2 shows a bottom elevational view of the device with a diaphragmassembly removed therefrom.

Fig. 3 shows a top view of the plastic housing.

Fig. ,4 shows a side view of the plastic housing.

Fig. 5 shows a sectional side view of the plastic housing taken alongthe line BB of Fig. 3.

Fig. 6 shows an exploded View illustrating the method of assembling thedevice shown in Fig. 1.

Fig. 7 is a typical graph showing the extended frequency response rangeof the improved sound translating device.

Referring now more particularly to the drawings, there is illustrated asound translating device in the form of a telephone receiver whichincludes a shield I formed from a magnetic sheet metal, such as steel,which acts as a magnetic shield for the device. Any extraneous foreignunwanted signals present will be prevented from interfering with thesound translation by means of this shield; and conversely, the fluxproduced by the magnetic field structure itself will be pre vented frominfluencing any other magnetic devices in proximity with the soundtranslating device. The cup shaped plastic housing 2, which, of course,could be constructed of any non-magnetic conductive material, is moldedwith the permanent magnet 3, preferably made of an aluminum nickelcobalt alloy having a coercive force greater than 500 oersteds and aremanence greater than 10,000 gausses, imbedded therein. T-shaped polepieces 4 and 5, preferably made of Allegheny electric metal, are alsopartially (the tops of the Ts) imbedded in the molding operation and arelocated one on each side of the permanent magnet 3 in a parallelrelationship. The lower portion of housing 2 flanges out and forms asmooth annular ring 6 for providing a bearing surface for receivingdiaphragm 5. Housing 2 also has scooped out recess portions 8 and 9 forenabling th magnetization of permanent magnet 3 after the device hasbeen. assembled, but before the shield is attached. Fig. 1 illustratesthis feature quite well as it can be seen that magnet 3 is accessiblefor a magnetizing operation any time until the shield I is affixed.Terminal assemblies [0 and II, preferably constructed of brass and alsomolded within housing 2, provide connecting points for th two leadscoming off the coils I2 and l3 as illustrated in Fig. 2. Holes l4 and l5 in housing 2 are provided in order that the cord tips of the two leads(not shown) extending to the receiver can be inserted to effect theconnection in a simple operation. This feature is best illustrated inFig. 5 where it can be seen that a cord tip inserted into hole It willmake connection with terminal l0 and, of course. one side of the coil.Holes l0 and I! are provided in order that set screws may be inserted toanchor the cordsin place. Rectangular opening H3 in the housing 2 isprovided in order that an anchoring means for the cords may be attachedfor transferring the burden of the cord strain from the terminals. Themagnetic field of the structure thus comprises the two pole pieces 4 andupon which the coils l2 and [3 of the receiver arepiwound andh apermanent magnet 3 which, inconjunction with the diaphragm] and the polepieces 4 and5, forms a substantially closed magnetic circuit interruptedonly by the narrow air gaps extending between the pole iacesa of thepieces 4 and 5 and the diaphragm]. The

coil winding i2 is wound upon the pole piece 5 between winding heads 31and SS; constructedof insulating material, and is insulated--from--the'= pole piece 5 by a layer of insulating material 41 which may, forexample, comprise \varnishedm tion to the diaphragm 1, "aninner" plateifly a clamp plate 28min annularasupporting andspace ring 2|, anassembly ring 22'; and a front cover 25, constructed of Bakelite inthewpresent em bodiment-,- witha i-fibrous damping member il iafilxedtheretos- The clamp .plate zllqis provided with aprojecting.annulariportionzmt having a smooth upper surface=which isadapted to cooperate with the oppositely disposed lower surface ot theannular ring portion 6 of the housing-2 to clamp the peripheral n edge.of the diaphragm 'r'l therebetween. The'clamping surfaces ofthgtwoannular portions 6 and M-areso formed that :the-

peripheral edge of:the"diaphragm] is clamped-v therebetween withuniformpressure at all points aroundthe outer circumferenceofthediaphragm.

Front cover 251*has a clamping"ring tlcmadeof aluminum in thepresentembodiment, molded into the Bakelite with theaid o'fsix'loondinev holes l 34, :and provides :a projecting ring for crimping inorder to hold said cover in place-as illustrated in Fig: 1. Inaccordancewith one-feature of the invention, the inner plate 19, inconjunctionzwith" the diaphragm l and the annular-ringfi, defines:

a damping chamber adjacent the: inner surface of the diaphragm -I, whiletheclamp plate 20,2 in" conjunction with the diaphragm"! 'andu'frontcover 25with damping member 26;: a souncbabe sorbent 'felt washer i-nthezpresent embodiment defines-a resonating chamber adjacent the outersurface of the diaphragm l. The dimensions of thedampingchamberuand oftherestricting passages communicating therewith are so proper-i tionedthat the peak ain the' response charactei isticof the device causedrbythe' natural periodof vibration of the diaphragm T is substantially;

r so characteristic of the .device.- 'More particularly;

reduced to flattenit-he overall frequency'response the inner plate l9;whichis constructedof nonmagnetic material, such, for example, asaluminum, is providedewithithree openings is and-has: mounted thereon inspacedapart relation a. hat;

annularwring Zhwhich defines a relatively long,

narrow, restricted and annuIar passage-2! "com-- municating between theinterior of the housing 2 and the chamber-formed by the inner plate l9and the-diaphragm I; By suitablyiproportioning the size of theholes23yaand the length'andwid-th i of the restricted passage 21;thereis achieveclthe desireddampingrr: efiect over. the 'rband gOf.:.frc'- quencies within which the natural period oi "vie braliionrofi-thewdiaphragm :1 is most i effective to Inches Diameter ofachamber1.688 Depth of chamber .020

Diameterof -holesrfl .076 Depth of passagezl .003 Widthof ring 24".;.319 Outer-diameter{ofaring 24 1.444

Theiinner plate l9 has formed therein a pair of slots 30 and 3| throughwhich the pole face ends of-t-he polepieces '4 and 5 extends A crossslot 32 connecting, thetwo' slots 3ll and :3 l \is also provided A forpreventing: the circulation ,of eddy currents in the inner-plate l9. Thedimensions of the slotswv 3E) and 3| aresubstantially greater thanlthecross sectional dimensions of-ithec-polet-face ends .oi the *pole:piecesl and 5 so thatrelatively larger, airxgaps are provided betweenthe a-djacentisur-t. faces of the: polepieces andzthei innemplate 19. ABy virtue of this-arrangement.theacouplingibem tween themagnetic circuitofsthe magnetic field structure and the-inner plate 19 is extremelyloose and the production of. eddy currents in ithetplate issubstantially prevented.

The front "cover 2 5, which, :in conjunction with the diaphragm- 1,damping. memberiZBHand clamps, plate 20, deflnesia resonatingchambenfadjacenta the outer surfaces of .the .diaphragm is provided withsix passages or,.ho1es 28 sthroughwwhich," sound waves are transmittedfrom. .tha resonating chamber. to the exterior of ..the ...device.....In.(ac1.., cordance with another .feature, of the. invention, thedimensions of this frontpresonating chamber and of the passages 28 .are.so .proportionedithatn the naturaliperiodof ivibrationiotthe chambersoccurs at approximately..4,000 cycles pe seconds;

whereby theresponse of themovinglsystemis mar.. terially, enhancedatfrequencies in that regional, However, in order to reduce theactualipeak, or-M dinarilyi produced. at the natural ,frequencyiof .a wresonating chamber vandlthus. in effect flatten .the i n response ,curvein thatcregion, damping member .i

26 utilized; To achieve this greater. and more uniform response in thefrequency region indicate ed,, it has ,beenifoundi. thatthe. following.dimensionswfor (theiresonating chamber and theipasm sages 72B aresatisfactory:

Inches.

Outer. diameter, of chamber. adjacent tdiae phragm 1.688; Maximum depthof chamber .093 Diameter of each passage 28, ,.102 Depthiofeachflpassage28 ,.050"

Insjidecdiametcr, of dampingrmember 26 Ire .625 0utside.,dia rneter. ofclamping member 2.6 ,1.188f Depth of damping member 265.1. .050-

In constructing the device described aboveythe plastichousing 2 is, ofcourse, flrs't'formed with magnet 3 andpole'wpieces 4 and 5'moldedthereimc The coils l2 and I3, connected in series at point: 36:(Fig. 2) with their associated swindingf heads 31, 38,? 39 "and 40,:are "then *-*inserted: over epolex; pieces '5 and 4 and cemented to thehousingnt. 2 The" two'i remainingrdeads :irom isaid pole lpiedesarcrsoldered to terminals iln andxl l."- 1' Artu -this field structureassembly is completed the diaphragm assembly is mounted upon the rim ofthe cup shaped housing 2. To this end, the inner plate [9 is forcedwithin the snugly engaging side walls of the annular ring 6 to abutagainst surface 35 of housing 2 and cemented to winding heads 31 and 30.This operation is [performed with the flat annular ring 24 mounted uponthe inner plate ill, by means of rivets and washers, and during theperformance thereof the pole face ends of the pole pieces 4 and 5 passthrough the slots 30 and 3! provided in the plate 19. The next step inthe construction of the device is to clamp the diaphragm 7 between theclamping surfaces of the two ring portions 6 and 29 pro- .jectingrespectively from the housing 2 and the clamp plate 20. While thediaphragm is clamped in position, the assembly ring 22 with the annularring 25 inserted or telescoped therein is telescoped over the clampplate 20 until the flange portion 44 thereof engages the tapered surfaceof the clamp plate 20, following which the rim of the assembly ring isbent or crimped over as indicated at 45 to engage the diaphragm assemblyrigidly secured to housing 2. The next step in the construction of thedevice is that of magnetizing the magnet member 3 by positioning this'member in a strong direct magnetic field. After the device is fullyconstructed shield l is placed over housing 2 and front cover 25, withdamp- 3 arranged in the manner set forth above, an attractive force isnormally exerted upon the diaphragm 1 by virtue of the flux produced inthe magnetic field structure by the permanent magnet 3. When incomingsignal current traverses the coils l2 and I3, the steady state flux isincreased and decreased in the usual manner in accordance with theundulations of the signal current. The variations in the flux traversingthe diaphragm 1 cause this diaphragm to vibrate in the usual manner sothat sound waves are transmitted by way of the passages 28 to theexterior. The provision of the inner damping chamber defined by theplate l9 prevents an excessive response of the diaphragm l atfrequencies approaching the natural frequency of vibration of thediaphragm-approximately 1,000 cycles per second. Also, the provision ofthe front resonating chamber, with the damping means, defined by thecover 25 enhances the response of the moving system at frequencies inthe upper .7

portion of the operatin range-approximately 4-,000 cycles. Thus, asubstantially flat response characteristic, as illustrated in Fig. 7,typifying good fidelity of reproduction, is obtained.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made herein, and it is intended to cover inthe appended claims all such modifications as fall within the truespirit and scope of the invention.

Having described my invention in detail, what I claim and desire to haveprotected by issuance of Letters Patent of the United States is:

1. In a sound translating device, a housing, a

diaphragm mounted within said housing, said diaphragm having apredetermined response characteristic over an operating frequency rangewhen mounted within said housing for substantially free vibration, saiddiaphragm also having a natural frequency of vibration such that saidresponse characteristic peaks at frequencies in the low frequency end ofsaid range, an inner plate mounted within said housing and displacedfrom said diaphragm to define a first chamber adjacent the inner side ofsaid diaphragm, means comprising a second plate mounted upon said innerplate in spaced apart relation for defining a passage communicating withsaid first chamber, the spacing between said plates being soproportioned that said first chamber acts substantially entirely as adamping chamber effective to remove said peak from the responsecharacteristic of said diaphragm at frequencies in the low frequencyregion of the range, means defining a second chamber adjacent the outerside of said diaphragm having a, passage communicating therewith, thedimensions of said last-mentioned passage being so proportioned thatsaid second chamber acts substantially as a resonating chamber effectiveto peak the response characteristic in the high frequency region therebyincreasing the range, and damping means comprising a sound absorbingmember within said second chamber rigidly mounted at a distance fromsaid diaphragm for removing said peak in the high frequency region thuseffecting uniform response over a greater range of frequencies.

2. In a sound translating device, a housing, a diaphragm mounted withinsaid housing, said diaphragm having a predetermined responsecharacteristic over an operating frequency range when mounted withinsaid housing for substantially free vibration, said diaphragm having anatural frequency of vibration such that said response characteristicpeaks at frequencies in the low frequency end of said range, an innerplate mounted within said housing and displaced from said diaphragm todefine a first chamber adjacent the inner side of said diaphragm, meanscomprising a second plate mounted upon said inner plate in spaced apartrelation for defining a passage communicating with said first chamber,the spacing between said plates being so proportioned that said firstchamber acts substantially entirely as a damping chamber to remove thelow frequency peak from the response characteristic of said diaphragmand substantially to decrease the response of said diaphragm atfrequencies within a band of frequencies extending from a frequency ofthe order of 1500 cycles per second toward the low frequency end of saidrange, a front cover for said device in spaced apart relation with saiddiaphragm to substantially define a second chamber adjacent the outerside of said diaphragm, an opening in the central portion of said covercommunicating with said second chamber, said opening being sodimensioned and proportioned that said second cham- K ber resonates andincreases the response of said diaphragm at frequencies within a band offrequencies extending from a frequency of the order of 3200 cycles persecond and such that the response characteristic peaks at a frequency of4000 cycles per second, and a sound absorbing annular damping membermounted on the inner side of said cover and completely removed from thediaphragm for removing the high frequency peak thereby effecting auniform response up to 4000 cycles per second.

v3. In arsound; translating, device, a molded housing having a-magneticfield structure includi ngla. bar magnetand apair of pole pieces moldedintb; the rear, section thereof, said pole pieces projecting into theinterior of said housins coils housing, adjacent the pole faces of saidbar magnet to facilitate magnetization of said bar magnet after theformation of-said sealed chamber.

4,; In a sound translating device. a molded bersalso molded intothe rearsection of said l m siitg,- coilsr; mounted on said pole pieces andelectrically connected to said terminal members,

a diaphragm structure and a front cover secured .tothe open end of saidhousing in spaced apart relation to form a sealed chamber to the rea ofdiaphragm structure and a resonating chamberforward of said diaphragmstructure, exter nal recesses insaid housing on oppositesides of saidbarmagnet to facilitate magnetization thereof after the formation of saidsealed chamber in order to prevent adherence of magnetic particles tosaid field structure during the as- ,8 .sembling, and externaltrecessesin said. housing on two sides of said terminal members toperm it accessthereto for: connections to, said coils.

5. In asound tr'ansiatingdevice as claimed in claim 4, a magnetic shieldenclosingsaid housing for preventing externalelectrical interferencesfrom influencing said field structure and to preventthe flux produced bysaid magnetic :field structure from: influencingother external, devicesin, proximity thereof.

Referencesfiited in the file ofthis patent UNITED STATES PATENTS NumberName Date;

1,415,361 Jones May 9, 1922 1,718,351 Gruber June 25, 1929 1,847,702Thuras Mar. 1,1932 2,110,908 Hartman Mar. I5, 1938 2,187,236 HansdorfJan. 16,, 1940 2,205,669 Pye June 25,1940 2,205,670 Pye June 25,19402,298,765 Horlacher Oct. 13, 1942 2,423,014 Gilman June 24, 19472,431,022 Brodie N 0V. 18,1947 2,458,158 Gilman Jan. 4, 1949 2,496,483Massa Feb. 7', 1950 F0REIGN- PATENTS Number Country Date 491,509 GreatBritain Sept'j5', 193B

